1. Field of the Invention
This invention relates to an image protective film. More particularly, the present invention relates to an image protective film that can in a simple way adequately protect the surfaces of images formed by various image recording processes, in particular, can also adequately protect the surface of an image formed by a sublimiation transfer system.
2. Description of the Related Art
Various methods for protecting image surfaces have been hitherto proposed in order to improve light resistance, moisture resistance, scratch resistance, etc. of images formed on paper, plastic film or the like. As a simple method that can be of everyday use a method is known in which a plastic film is merely adhered on an image surface by the use of an adhesive, or a material coated with a hot-melt adhesive is contact-bonded to a base film under application of heat.
With the recent widespread use of prepaid cards, ID cards, membership cards, etc., such protection of image surfaces has become popular also when such cards are prepared. Then, there is an increasing demand for making it feasible not only for those who are engaged in image formation or card preparation but also those who distribute cards or use cards to easily apply a means for the protection of the cards.
Such conventional methods for the protection of image surfaces, however, have been unable to adequately protect images formed by any image recording processes. That is to say, according to conventional methods commonly used, a frame is formed around an object article (an article to be protected) such as a card on which an image has been formed, so that the article to which the protection has been applied has a larger size than the original one. Hence, the cards often become inconvenient to carry, and also, in the case of those which are strictly regulated on their shapes in use as exemplified by prepaid cards, there have been problems such that a card can not be inserted to a fixed card inlet or the card can not function as a card.
Some of conventional methods include a method in which no frame is formed around the object article. Such a method, however, has required a troublesome operation because, after a protective film has been pasted to the image surface of the object article, the film protruding from the article must be cut off in a separate step.
In addition, in conventional methods, plasticizers are used in the protective films and adhesives that come into contact with the image surfaces, the plasticizers for the purpose of imparting flexibility to the films. Hence if, for example, any conventional method is applied for the surface protection of an image formed by thermal recording of a sublimation transfer system as in thermal transfer, an extreme migration of dyes may occur on the image surface to rough the surface and also cause bleeding of image or fading at an early stage. Also when the method is applied to an image surface formed by a melt transfer system, the migration of dyes as in the case of the protection of the image surface formed by the sublimation transfer system does not occur, but blocking may occur. Thus, any of the conventional methods can not also be a method that enables satisfactory protection of image surfaces in that case.
Meanwhile, the image recording method according to the thermal transfer system allow use of a compact apparatus which requires only simple maintenance. Hence, this system is widely used. In particular, the sublimation transfer system can provide an image with excellent gradation, and in recent years has become prevalent as an image forming method when images are recorded in full colors. Hence, the conventional methods that can not well protect the image formed by the sublimation transfer system have been considered very unsatisfactory as a method for the protection of such image surfaces.